Automobiles and other automotive vehicles have electrical systems powered by an on-board battery for controlling the starter motor, ignition systems, lighting, other accessories and the like. For a number of years, such automotive electrical systems have typically been powered by 12-volt battery, the actual operating voltage of such systems being about 14 volts with reference to charging voltages. A number of different types of portable, hand-held circuit testers have been developed for testing such automotive electrical systems, which testers are calibrated to operate in a voltage range suitable for a nominal 14-volt system, which range typically runs from zero to about 20 VDC.
The automotive industry is presently developing a new automotive electrical system which will be capable of operating from both the traditional 12-volt power system and a proposed 36-volt power system, which will have an actual operating voltage of about 42 volts with reference to charging voltage. This will require development of circuit tester tools calibrated to the proposed 42-volt electrical systems, yet 14-volt system testers will also be needed for many years to come.
The automotive industry has established various standard voltage levels for both the 14-volt and 42-volt systems, including such voltages as minimum start voltage, minimum voltage-engine off, maximum voltage-engine off, maximum voltage clamp, as well as the nominal voltage for the system operation. Existing hand-held circuit testers are designed to simply indicate hot or ground circuits or high or low logic levels, and do not indicate plural specific voltage levels. Meters or testers are, of course, available which will measure precise voltages or multiple voltage levels, but they are typically larger and more complex devices and are not designed for hand-held probe-type use.
This application discloses a circuit testing apparatus and method which avoids the disadvantages of prior circuit testers while affording additional structural and operating advantages.
An important aspect is the provision of an automotive circuit tester which can indicate plural discrete voltage levels in different voltage ranges.
Another aspect is the provision of a circuit tester of the type set forth which is of simple and economical construction.
A still further aspect is the provision of a circuit tester of the type set forth, which is capable of testing high-impedance circuits without significantly loading them.
Another aspect is the provision of a circuit tester of the type set forth, which automatically turns the tester on in the presence of an input voltage.
Certain ones of these and other aspects may be attained by providing a portable hand-held automotive circuit tester for detecting voltages in different voltage ranges corresponding respectively to different-voltage automotive electrical systems, the tester comprising: a housing having a probe tip and a ground connector projecting therefrom and having plural groups of indicator apertures therein respectively corresponding to plural different voltage ranges; and a voltage detector disposed in the housing and including an input circuit coupled to the probe tip and producing an input signal from the circuit being tested, a power supply circuit, a reference circuit coupled to the power supply circuit and producing a plurality of reference signals arranged in sets corresponding to the plural different voltage ranges with each set incrementally graduated from a low amplitude to a high amplitude, a comparison circuit coupled to the input circuit and to the reference circuit and to the power supply circuit and comparing the input signal to each of the reference signals, and plural groups of indicators respectively corresponding to the sets of reference levels and respectively viewable through the groups of apertures and coupled to the comparison circuit so that only one group of indicators will be operable, depending on the voltage of the automotive electrical system being tested, the comparison circuit being responsive to the input signal for energizing the indicator corresponding to the highest reference level which the input signal equals or exceeds.